a. Field of the Invention
The invention relates generally to the field of medical instruments, and more particularly to a medical instrument for introduction into a body, such as a catheter, diagnostic catheter, ablation catheter, pacemaker, and internal cardiac defibrillator, that employs a flexible printed circuit to convey signals or energy along the medical device. The invention also relates to manufacturing methods for producing such medical instruments.
b. Background Art
Catheters have been used for medical procedures for many years. Among other uses, physicians use catheters to examine, diagnose, and/or treat tissue while positioned at a specific location within the body otherwise inaccessible without more invasive procedures. Increasingly, catheters are used for medical procedures involving the human heart.
As illustrated in FIG. 1, a typical human heart 10 includes a right ventricle 12, a right atrium 14, a left ventricle 16 and a left atrium 18. The right atrium is in fluid communication with the superior vena cava 20 and the inferior vena cava 22. The interatrial septum 24 separates the right atrium from the left atrium. The tricuspid valve 26 provides a fluid flow path between the right atrium and the right ventricle. On the inner wall of the right atrium where it is connected with the left atrium is a thin walled, recessed area, referred to as the fossa ovalis 28. Between the fossa ovalis and the tricuspid valve is the opening or ostium for the coronary sinus 30. The coronary sinus is the large epicardial vein which accommodates most of the venous blood which drains from the myocardium into the right atrium.
In a normal heart, contraction and relaxation of the heart muscle (myocardium), i.e., the “heart beats,” takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node (not shown) located in the right atrium 14 to the atrialventricular (AV) node (not shown) and then along a well defined route, which includes the His-Purkinje system, into the left 16 and right 12 ventricles. Normally, initial electric impulses are generated at the SA node and conducted to the AV node. The AV node lies near the ostium of the coronary sinus 30. The His-Purkinje system begins at the AV node and penetrates the membranous interatrial septum 24 into the membranous interventricular septum 32. At the basilar aspect (or upper aspect/superior aspect) of the interventricular septum, the His-Purkinje system splits into right and left branches which straddle the summit of the muscular part of the interventricular septum.
Sometimes abnormal rhythms occur in one or both atria which are referred to as atrial arrhythmia. Three of the most common arrhythmia are ectopic atrial tachycardia, atrial fibrillation and atrial flutter. Atrial arrhythmia can have various impacts on a patient. For example, atrial fibrillation can result in significant patient discomfort and even death because of a number of associated problems, including the following: (1) an irregular heart rate, which causes a patient discomfort and anxiety, (2) loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure, and (3) stasis of blood flow, which increases the vulnerability to thromboembolism and the associated risk of stroke.
It is sometimes difficult to isolate a specific pathological cause for the atrial fibrillation although it is believed that the principal mechanism is one or a multitude of extra circuits within the left and/or right atrium. These extra circuits, which are also sometimes referred to as extra electrical pathways, may interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles. Efforts to alleviate these problems in the past have included significant usage of various drugs. In some circumstances drug therapy is ineffective and frequently is plagued with side effects such as dizziness, nausea, vision problems, and other difficulties.
A procedure, oftentimes referred to as “mapping,” utilizes a catheter with sensing electrodes to monitor various forms of electrical activity in the human body. Various organs, including the heart and brain, may be mapped by a catheter having appropriate diagnostic functions. Through mapping, a physician can, in some instances, detect the extra electrical pathways believed to cause the abnormal rhythms. Moreover, the physician can determine the presence or general location of the pathways.
Upon detection of extra pathways causing an irregular heartbeat, an increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia and atrial arrhythmia uses a catheter to convey energy to a selected location within the heart to cauterize or necrotize cardiac tissue and thereby cut off the path for extra or improper electrical signals. This procedure is often referred to as an “ablation” of cardiac tissue. Typically, the ablation catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, through an introducer, through the vessels until the ablation catheter reaches the desired location for the ablation procedure in the heart. One type of ablation catheter commonly used to perform ablation produces lesions or small burns that electrically isolate or render the tissue non-conductive at particular points in the cardiac tissue by physical contact of the cardiac tissue with an electrode of the ablation catheter and application of energy, such as radio frequency energy. The lesion partially or completely blocks the extra electrical pathways to lessen or eliminate arrhythmias.
In some respects, mapping may be thought of as the opposite of ablation. Specifically, a mapping catheter detects bioelectric impulses generated by the tissue in question and relays these bioelectric impulses to a diagnostic machine operably attached to the catheter. Accordingly, instead of transmitting energy to tissue, the mapping catheter transmits signals from the tissue and can be read in the form of voltages.
Regardless of the direction of energy transmission, present catheters generally mechanically mount the bioelectric receivers and energy delivery media, such as electrodes, to the catheter surface. Further, the transmission media, typically one or more wires, is generally strung through an opening in the center of the catheter, and is not attached to the catheter save at the connection point with the electrodes. Accordingly, as the catheter is steered, bent, and moved during a procedure, stress may be applied to the internal wires.
In some instances, a catheter may also provide a conduit by which other catheter or medical devices are inserted into a patient. When medical instruments are inserted into the catheter interior, the surgeon must exercise some degree of care to ensure the instruments do not interfere with the diagnostic functions of the catheter or, possibly, damage the wires.
Catheters used in mapping and ablation can be very small in diameter. For example, some catheters are as small as 2 to 6 French (1 French=0.3 mm), and can be smaller. As such, assembly of a catheter, such as connecting wires to the electrode and stringing those wires through the catheter can be difficult. In some instances, due to the difficulty in adhering the wires to the electrodes, defective catheters may be produced, resulting in poor signals, waste and lowered manufacturing efficiency.
Oftentimes it is necessary to drill or pierce holes through the catheter in order to connect the wires to electrodes. If not properly sealed, fluid can seep into the holes and cause distortion of the signals, cause shorting, and cause other problems.
Further, many diagnostic and energy delivery catheters have multiple wires running to a variety of diagnostic or energy delivery sites. At the catheter's distal end, these wires often simply terminate with little or no identification separating one wire from the next, making attaching a wire to the appropriate connector pin of a medical device difficult. Apparatus leads, such as pacemaker leads, often suffer from similar problems. Leads may be used to deliver energy to tissue, typically in order to regulate tissue contraction through timed pulses of electricity. Such regulation may occur, for example, by a pacemaker or ICD.
Accordingly, there is a need for an improved medical device capable of transmitting electrical energy across its length either to or from a target site.